The genus Bacteroides is a member of the family Bacteroidaceae. They are Gram-negative, obligately anaerobic, nonsporeforming rods. The genus contains at least 39 species, and are often isolated from sewage as well as the digestive tract of man, animals, and insects. Bacteroides fragilis was first described in 1898 by Veillon and Zuber, but was called Bacillus fragilis. In 1919, Castellani and Chalmers transferred it to the Bacteroides genus. The “B. fragilis group” refers to the saccharoelastic bacteroids that grow well in bile. Members of this group were previously subspecies of B. fragilis and include B. fragilis, B. distasonis, B. ovatus, B. thetaiotaomicron, and B. vulgatus (Castellani and Chalmers. 1984. Genus I. Bacteroides 1919, 959. Krieg and Holt (editors) In Bergey's Manual of Systematic Bacteriology, 1:604–631).
Bacteroides fragilis accounts for only 1% of the normal flora of the human colon, but is the most common anaerobe isolated from clinical specimens. It is associated with soft tissue infections, abscesses and bacteremia (Moncrief J., et al, 1998. Infect. Immun. 66:1735–1739). B. fragilis has also been associated with infection of the skeletal muscle (Katagiri, K., et al, 1996. J. Dermatology. 23:129–132), and meningitis (Aucher, P., et al, 1996. Eur. J. Clin. Microbiol. Infect. Dis. 15:820–823). The B. fragilis group is responsible for 65% of all anaerobic bacteremia cases, with mortality rates in excess of 19% (Redondo, M., et al, 1995. Clinical Infectious Disease. 20:1492–1496).
In 1984, strains of B. fragilis were found to cause diarrhea in newborn lambs (Myers, L., et al, 1984. Infect. Immun. 44:241–244). Subsequently, it has been shown that B. fragilis is associated with diarrhea in other livestock and young children. These strains are called enterotoxigenic strains, because they produced a 20 KD metalloprotease enterotoxin with intestinal secretory activity (Moncrief J., et al, 1995. Infect. Immun. 63:175–181).
There has been an increase in antibiotic resistance within the Bacteroides fragilis group. While there is still excellent activity of many antibiotics, even some of the most potent agents, the carbapenems and the β-lactamase-inhibitor combinations, are losing activity (Snydman, D., et al, 1996. Clinical Infectious Diseases. 23:S54–65). The cefoxitin resistance rate has increased from 0% in 1987 to 22% in 1995 (Bianchini, H., et al, 1997. Clinical Infectious Diseases. 25:S268–269). Resistance to metronidazole, co-amoxiclav, and imipenem is rare, but strains have been found that are resistant to one or all of these antibiotics. (Turner, P., et al, 1995. The Lancet. 345:1275–1277). Clindaycin resistance has been shown to be transferred between strains by either plasmid or transposon mechanisms. (Dalmau, D., et al, 1997. Clinical Infectious Diseases. 24:874–877). The increasing resistance to antibiotics commonly used against Bacteroides species may eventually lead to failures of these treatments.
Sequencing and analysis of this genome is crucial for the identification of essential genes for development of drug targets and to reduce the emerging health threat this organism poses.